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Is it a good idea to get a recommendation from a friend with whom I have worked in a couple of social welfare organizations?

Nowhere near as good of an idea as getting a professor to write one.

It's not the best idea. Unless you've been out of school for a long while, the hierarchy of LOR writers is pretty much:
professors>>boss/supervisor>>>coworker.

Beyond the fact that this friend will only be able to evaluate you as a peer, I would worry about the friend's ability to write maturely and objectively enough to even sound like a coworker. The last thing you need is a letter that sounds like it was written by your best friend claiming to know you on a professional basis.